tracing/boot: Add instance node support

Add instance node support to boot-time tracing. User can set
some options and event nodes under instance node.

 - ftrace.instance.INSTANCE[...]
   Add new INSTANCE instance. Some options and event nodes
   are acceptable for instance node.

Link: http://lkml.kernel.org/r/157867242413.17873.9814204526141500278.stgit@devnote2Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_boot.c

@@ -20,7 +20,7 @@ extern ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
 					  unsigned long size, int cpu_id);
 
 static void __init
-trace_boot_set_ftrace_options(struct trace_array *tr, struct xbc_node *node)
+trace_boot_set_instance_options(struct trace_array *tr, struct xbc_node *node)
 {
 	struct xbc_node *anode;
 	const char *p;
@@ -242,6 +242,40 @@ trace_boot_enable_tracer(struct trace_array *tr, struct xbc_node *node)
 	}
 }
 
+static void __init
+trace_boot_init_one_instance(struct trace_array *tr, struct xbc_node *node)
+{
+	trace_boot_set_instance_options(tr, node);
+	trace_boot_init_events(tr, node);
+	trace_boot_enable_events(tr, node);
+	trace_boot_enable_tracer(tr, node);
+}
+
+static void __init
+trace_boot_init_instances(struct xbc_node *node)
+{
+	struct xbc_node *inode;
+	struct trace_array *tr;
+	const char *p;
+
+	node = xbc_node_find_child(node, "instance");
+	if (!node)
+		return;
+
+	xbc_node_for_each_child(node, inode) {
+		p = xbc_node_get_data(inode);
+		if (!p || *p == '\0')
+			continue;
+
+		tr = trace_array_get_by_name(p);
+		if (IS_ERR(tr)) {
+			pr_err("Failed to get trace instance %s\n", p);
+			continue;
+		}
+		trace_boot_init_one_instance(tr, inode);
+	}
+}
+
 static int __init trace_boot_init(void)
 {
 	struct xbc_node *trace_node;
@@ -255,10 +289,9 @@ static int __init trace_boot_init(void)
 	if (!tr)
 		return 0;
 
-	trace_boot_set_ftrace_options(tr, trace_node);
-	trace_boot_init_events(tr, trace_node);
-	trace_boot_enable_events(tr, trace_node);
-	trace_boot_enable_tracer(tr, trace_node);
+	/* Global trace array is also one instance */
+	trace_boot_init_one_instance(tr, trace_node);
+	trace_boot_init_instances(trace_node);
 
 	return 0;
 }